Ok, I’d heard with a smooth barrel you didn’t need a choke but wanted to sure. I’ve never used one beforeAlways have a choke tube installed. Shooting without a choke tube could damage the threads.
Yes with slugs is usually good idea to start with your most open choke, but don't be afraid to try tighter choke tubes to see if you get better groups. My 3-Gun Rem 1100 shoot Remington Sluggers best using a modified choke but does better with an improved cylinder when shooting Wolf Slugs.